Multiple Inverter System for Electric Machine DC Bus Ripple
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Solution Overview
Problem
The increased current demand by inverters for electric machines leads to fluctuating DC bus currents, requiring larger and more costly capacitors to manage, which is inefficient and costly.
Innovation Solution
Implementing a multiple inverter system with phase-offset PWM signals generated by gate drivers, where the phase shift of carrier and fundamental waveforms is adjusted based on the electric machine's speed and phase offset to minimize current ripple in the DC bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If inverters demand more input current to increase power available to electric machines, then the power output of the electric machine is improved, but the DC bus experiences increased fluctuating current requiring larger capacitors
Solution Approach 1:
The patent divides the single inverter system into multiple inverters (first inverter and second inverter) that share the power delivery to the electric machine. Each inverter handles a portion of the total power, which segments the current draw from the DC bus. This segmentation reduces the fluctuating current magnitude on the DC bus compared to a single inverter system, allowing for smaller capacitor sizes while maintaining the required power output.
2Stability of the object's composition
If larger capacitors are used to compensate for fluctuating DC bus current, then the stability of the DC bus is improved, but the system cost and complexity increase
Solution Approach 1:
Instead of using a single large capacitor to stabilize the DC bus, the patent segments the power delivery function across multiple inverters. This segmentation naturally reduces the current ripple and fluctuation on the DC bus, thereby reducing the stabilization burden on individual capacitors. The result is a system that achieves DC bus stability with smaller, less complex capacitor arrangements.
3Quantity of substance
If multiple inverters are implemented to reduce current ripple, then the capacitor size is optimized, but the inverter system complexity increases
Solution Approach 1:
The patent merges the control functions of multiple inverters through a coordinated control system that manages phase-offset PWM signals for both inverters. This merging of control functions allows the system to achieve current ripple reduction benefits while using standardized inverter modules. The coordinated control enables the multiple inverters to work together as an integrated system, optimizing capacitor sizing without requiring completely custom inverter designs.
Data Source
AI summary
A vehicle may include an electric machine including windings having a nonzero phase offset. The vehicle may further include first and second inverters configured to drive the electric machine as a result of toggling of switches. The switches may be toggled according to respective pulse width modulation (PWM) signals. One or more gate drivers may be configured to generate the PWM signals. The PWM signals may be based on fundamental waveforms having a phase shift that is based on the nonzero phase offset of the electric machine.